The long term objective of this proposal is to develop a commercial subunit vaccine for human respiratory syncytial virus (RSV). Because of the high cost of preparing these glycoproteins, a means for achieving an enhanced immune response is an important objective, and is the focus of this proposal. biocompatible and biodegradable microspheres consisting of a copolymer of DL-lactide and glycolide (poly DL-lactide-co-glycolide) will be utilized to incorporate RSV antigens into small spherical particles (1-10 um). Microspheres containing viral antigens will be used for subcutaneous, intranasal and oral immunization of experimental animals, and their immune response will be evaluated. A different group of animals will be similarly immunized with inactivated virus in solution for comparison. If a significant enhancement in the protective immune response is observed using microencapsulated RSV antigens, more detailed studies will be subsequently pursued. Studies will also be conducted to understand the mechanism of protection (cellular/antibody mediated), and the duration of such response. Finally, microencapsulated virus envelope glycoproteins will be utilized for a clinical field trial for immunoprophylaxis against infection from RSV.